How it is supposed to work
 

SpaceShipTwo: How it's Supposed to Work : Discovery News

Granted that this source is credible, it gets more confusing.


Once unlocked the tail is not held in place by the pneumatic system, but by aerodynamic pressure on the tail?? Or does it mean that the pneumatic system is not powerfull enough to hold it in place when arrodynamic loads exceed a given limit?
I tried to follow the logic in the patent, while the unlocking is explained in great detail, there is not that much info on the working of the tilting system itself, or I was not able to grasp it.


Aerodynamic loads on the tail are not only influenced by speed (subsonic, transonic, supersonic) and altitude (less loads higher up), but also by shift of CG due to burnt fuel. According to the source that leads to a reversal of lifting force on the tail. after burn out. If I follow that logic, then the unlocking of the system would not only depend on the airspeed, but also on the remaining rocket fuel.

That must be a hell of a ride for the pilots to keep that ship pointed on the intended flightpath, now i understand these flight path oscilations some more.

Does that also mean, that unlocking the feathering system at 1.4M gives the tail some freedom to align with aerodynamic loads and thus helps in dampening the flightpath?

Any thouhts on that?

- I am totally confused by what we know so far of the tail 'feathering' system, but I think we must assume the tail movement is 'powered' somehow, and I can see significant aerodynamic forces moving the tail to 'feather', but I cannot see how the reverse will happen - unless the 're-entry' is inverted.

I too am confused, but some items in the patent seem to clarify some points and raise others.

So it seems that:
- Intentional feathering and un-feathering is by pneumatic upward and downward actuation.
- The feathering lock is re-applied as soon as the downward actuation is completed.

Leaving the following questions open:

- What keeps the booms in the feathered position, as there is no locking mechanism for this.
--- Pneumatic pressure?
--- Aerodynamic forces?

- What keeps the booms in the unfeathered position after unlocking, but prior to feathering?
--- Aerodynamic forces? But only in appropriate flight regimes?
--- Pneumatic pressure? But have the downward actuators been pressurized yet?

Actuators
 

It looks to me like Cylinder 33 controls the tilt. In the diagram it appears much larger the Cyl 41. From the description, I infer that 33 and 41 have the ability the ability to both push and pull rather than rely on some outside force (aerodynamic in the case of 33 and maybe a spring like force - like a leaf sping - in the locking hook in the case of 41) for one direction. If I'm right, then the pneumatic systems have the ability to apply differencial or equal pressure to both sides of the piston.

Applying equal pressure to both sides of the piston would "lock" the piston in place, but only up to a certain force because the air inside is compressible.

Under this scenario, 33 might provide stability above Mach 1.4, but be overcome (depending upon altitude) by aerodynamic forces in the transonic zone.

Another possibility is that a pneumatic failure in 41 could have caused a premature unlock and the pilot was moving the unlock lever to try to fix it.

I'll be reading the NTSB final report with interest.

With the additional insight from the Discovery News ref. (RetiredF4 post)

So not only must a sufficient Mach number have been reached (to be clear of the complex dynamics of the transsonic regime), also a sufficient CoG forward shift must have been made.

The Mach number 1.4 in the applicable flight regimes appears to imply both proper "clean" supersonic conditions and the required CoG for tail surfaces down-lift in that regime.

Which suggests that after "the (initial) boost phase" the aerodynamic forces cannot overcome the pneumatic downforces on the feather. Which would imply that positive lift on the tail surfaces up to a certain magnitude can be tolerated. Such positive lift occurances (assumed limited in time and magnitude) may result from the trim of the horizontal tail surfaces, elevon deflections and thrust vector variations (e.g. due to uneven burn and outflow).

Some numbers related to force and stroke had been found by PeterH, with an estimate of tail boom dimensions (someone may have these?) these numbers may then be related to maximum adverse (positive) lift on the tails that can be tolerated.

Which may serve to answer part of the recent questions from PeterH.

And leaves the following questions:
In line with the previous I would expect Yes and Yes. In addition the proper re-entry attitude relative to flight path - when not controllable aerodynamically - may be set up by the reaction control gas jets.

@thcrozier
A hard locking in any halfway position is not possible with pneumatics, and I would not expect the feathers to be in any other position than their extremes except when transitioning. Maintaining some pressure on the retreating side of the piston may serve though to smoothen the transition. In the feathered position I can imagine - rather than bi-lateral pressurisation - a uni-lateral pressurisation pressing against a hard mechanical stop.

@BOAC
I understand the the unfeathering motion to be driven by the pneumatics, possibly assisted with forward trimming of the horizontal stabilisers and up-deflection of the elevons to reduce required forces.

Upon inadvertant failure of the pneumatics during the unfeathering phase perhaps a roll to (partial) inverted attitude may be an emergency option (inside or outside of designed procedures). I recall this trick had been pulled by an aeroplane with structural wing failure (distant past, must search deep ...).

Other than that: bail out at safe altitude and speed.

It would be interesting to know if parachutes are forseeen for space flight passengers (?)

janrein

At the risk of thread drift I guess you mean this:

Zlin wing Structural Failure Report - Neil Williams

unplanned test pilot flights
 

Oh yeah, the aerobatic pilot's famous inverted approach and crash.

As with me on my Viper leading edge flap failure ride, you have to remain as calm as possible and see what works and what doesn't. But you don't have a minute, or even a few seconds in some cases. As with the aerobatic dude, I was flying fast enough to have a small degree of roll control and plenty of yaw, even with the right LEF folded up at 50 or 60 degrees. So don't do something stupid, just sit there!!! Don't slow down, don't go faster, don't pull up, don't roll, just stay there while the gal is happy.

http://sluf.org/misc_pages/rightwing.jpg


The SS2 guys didn't have a chance. And I seem to recall Mel unlocking the feather mechanism on his severe rolling ride for first leg of the X-prize. Alleged reason was for "dampening" or such.

I do not like allowing or depending on my control surfaces to move on their own. Just my preference, but I have reasons. Even at M 2, the SS2 should be able to shut down the motor and come back safely. Problem is the sucker goes ballistic at "x" altitude/"x" speed, and you are along for the ride to apogee. I would guess that the RCS might be used at or slightly above 100K with motor still running at a low setting, but once that motor shuts down for good you're screwed. Not sure about SS2 nozzle gimbals such as shuttle had. Dick Covey and John Blaha told me that the "return to launch site" procedure was a pipe dream, but they practiced it anyway because the main motors could be gimballed and throttled way back. Imagine rotating a zillion pounds of vehicle using the remaining fuel, main motors and OMS system and then gliding back home, heh heh.

Lastly, I do not understand the procedure to unlock the feathers early except it appears that the mechanism is pneumatic, not pure mechanical. Why not a simple cable and long handle to rotate those big hooks? Leverage. Ditto for deploying the feathers coming back. But maybe loads on the feather suckers require a huge mechanical advantage as they are exerting pressure against the locking hook.

I am sure we will see some design and procedure changes, ya think?

@wiggy
Quick find!
And I would say relevant (admitted remotely) to the SS2 mission.

Consequences of the crash and / or disagreement how or if to proceed further?

http://www.virgingalactic.com/introd...ond-spaceship/